In the packaging of spent nuclear fuel from nuclear reactors for dry storage or shipment, the primary concern is with the reliable containment of the radioactive nuclear fuel in order to prevent unwanted exposure to radiation. To ensure this protection, the container or canister, and its associated surrounding cask, must meet several criteria. The container must provide containment integrity to prevent the release of radioactive material during normal or hypothetical accident conditions, as well as structural integrity in supporting the weight load of the contained fuel. Thermal protection is required to provide adequate dissipation of the decay heat produced by the spent nuclear fuel, to avoid compromising the integrity of the fuel or the materials of the container or cask. Adequate radiation shielding must also be provided to limit the radiation field external to the package to acceptable values. The container must also protect against the possibility of nuclear criticality, since the contained fuel could represent a critical mass if the system's engineered features were removed or sufficiently degraded, or if the fuel geometry were radically altered through structural degradation.
The containers are sealed upon loading, often by double welding, so that re-entry to perform measurements is often not an acceptable option. Instrumentation penetrations are generally regarded as unacceptable because of increased risk of confinement system failure. Because of the uniformity in the manufacture of such systems, monitoring may be performed on a statistically acceptable subset of containers for a given fuel type, to ensure safety of the entire population of containers.
Currently, only coarse methods of monitoring are available, for fuel in dry storage. In some metal cask systems, the performance of metallic O-rings is monitored, to ensure seal integrity. In concrete cask systems in which air flow occurs, periodic monitoring of air outlet temperature is conducted.
The present invention has been developed in view of the foregoing, and to overcome other deficiencies of the prior art.